FIG. 1 shows a conventional computer 10 of the type that is adapted to be held in the hand H of an operator during use. Such computers 10, known as “palmtop” computers, include a relatively large display screen 12, and a few manually actuated keys, generally indicated as 14. The display screen 12 is preferably a touch screen that primarily controls the operation of the computer 10. More particularly, several icons 18 are displayed on the screen 12, and programs or other functions are selected by touching the screen 12 on the icon 18 corresponding to the program or function to be selected.
The basic components of the computer 10 are shown in the system block diagram of FIG. 2. The computer 10 includes a processor 20 of conventional design that is coupled through a processor bus 22 to a system controller 24. The processor bus 22 generally includes a set of bidirectional data bus lines coupling data to and from the processor 20, a set of unidirectional address bus lines coupling addresses from the processor 20, and a set of unidirectional control/status bus lines coupling control signals from the processor 20 and status signals to the processor 20. The system controller 24 performs two basic functions. First, it couples signals between the processor 20 and a system memory 26 via a memory bus 28. The system memory 26 is normally a dynamic random access memory (“DRAM”), but it may also be a static random access memory (“SRAM”). Second, the system controller 24 couples signals between the processor 20 and a peripheral bus 30. The peripheral bus 30 is, in turn, coupled to a read only memory (“ROM”) 32, a touch screen driver 34, a touch screen input circuit 36, and a keypad controller 38.
The ROM 32 stores a software program (described below) for controlling the operation of the computer 10, although the program may be transferred from the ROM 32 to the system memory 26 and executed by the processor 20 from the system memory 26. The touch screen driver 34 receives information from the processor 20 and applies appropriate signals to the display 12 through the touch screen driver 34. The touch screen input circuit 36 provides signals indicating that an action has been taken to select a program or function by touching the screen 12 on a corresponding icon 18 (FIG. 1). Finally, the keypad controller 38 interrogates the keys 14 to provide signals to the microprocessor 20 corresponding to a key 14 selected by an operator.
Returning, now, to FIG. 1, most palm computers, such as the computer 10, include a stylus (not shown) adapted to select the icons 18 displayed on the screen 12. The stylus has a relatively small point thereby allowing icons 18 displayed on the screen 12 to be selected even though the icons 18 may be relatively small and/or positioned close to either other icons 18 or the edges of the screen. However, the use of a stylus can be inconvenient because it is necessary to obtain the stylus, such as by removing it from a receptacle at the back of the computer 10, before any function can be selected.
To avoid the inconvenience of using a stylus, many operators use their fingers to select icons 18 on the screen 12 of the computer 10. While being more convenient, the use of a finger to select icons 18 creates other problems. Any finger is several orders of magnitude larger than the point of a stylus. It can therefore be difficult to select fine and/or closely spaced icons or features on the screen 12 using a finger. The location on the screen 12 that is selected by a finger is generally a point at the center of the area of the finger that is in contact with the screen. This point is sometimes known as the “hot spot”. With reference to FIG. 3, a finger F is shown touching the screen 12. The area A of contact between the finger F and screen 12 is somewhat smaller than the size of the finger F. The computer 10 then calculates a hot spot H at the center of the area of contact A. The hot spot H is small enough to be capable of accurately selecting even the finest and most closely spaced of icons 18 or other features displayed on the screen 12. However, this capability is not realized in practice because the hot spot is not displayed on the screen 12 as a cursor or other indicator. Further, even if a cursor was displayed on the screen 12 to designate the hot spot, the cursor would be beneath the finger F and thus not visible to the operator. Thus, in practice, it is often not possible to select fine and/or closely spaced icons 18 or features on the screen 12 using a finger F.
One approach that has been used to allow icons to be easily selected on touch screens is to display substantially larger icons 18 and features so that there is no ambiguity about which icon 18 or feature is being selected. While this approach does make it easier to select icons and features, it has the disadvantages of requiring that the operation of the computer 10 be altered and reducing the number of icons 18 and features that can be displayed on the screen 12 at the same time.
Another limitation of using a finger to select icons 18 and features on computer touch screens 12 is the difficulty of selecting icons or features that are near the edges of the screen 12. With reference to FIG. 4, a finger F′ is attempting to select an icon 18′ that is adjacent to one edge 40 of the screen 12. The finger F′ is centered over the icon 18′, but is overlapping the edge 40 of the screen 12. As a result, the area of contact A′ between the finger F′ and the screen 12 is offset to the left of the center of the finger F′ and so is the hot spot H′. Therefore, even though the user has centered his or her finger F′ over the icon 18′, the hot spot H′ is offset from the icon 18′. For this reason, a program or function corresponding to the icon 18′ will not be selected. This problem may continue even if the finger F′ is moved further to the right of its position shown in FIG. 4 because the hot spot H′ will always be located midway between the left edge of the area A′ of contact between the finger F′ and the screen 12 and the edge 40 of the screen 12. As a result, it may not be possible to position the hot spot H′ at or very close to the edge 40 of the screen 12. While the problem is shown in FIG. 4 in the context of selecting an icon 18′ adjacent the right edge 40 of the screen 12, it will be understood that the same problem occurs when selecting an icon that is positioned adjacent the left edge, the top edge, the bottom edge, or a corner of the screen 12.
While the foregoing discussion has centered around the problem of selecting icons and features on a touch screen displays for palmtop computers like the computer 10 shown in FIG. 1, the problem may also exist to some extent with selecting icons and features on full size touch screen computer displays.
There is therefore a need for a computer touch screen that allows a finger to accurately select icons and other features even where the icons or features are small and closely spaced, and even where they are at or very close to the edges of the screen.